Frequency-Dependent Conductivity. Ionic Conductivity and Memory Effects in Glassy Electrolytes

Ionic conductivities in glass depend very strongly on temperature, frequency and glass composition. In the absence of well-defined structure, the behaviour of vitreous electrolytes may be strongly influenced by various “memory effects”. These include the classical ion-atmosphere effect which tends to return ions to their starting positions – and hence causes a reduction in ion mobilities – and a newly formulated site memory effect, which effectively creates “cation vacancies”, and leads to conductivity enhancement. The site memory effect gives a straightforward explanation for compositional variations in conductivity (including the mixed alkali effect) and points up a connection with “strength” and “fragility” concepts of glass/melt structure.